Tips to fighting parasite infection in bovines Living just a couple of hours’ drive from the Mexican border, Joe Paschal enjoys the balmy weather of mid-January in southern Texas. He can’t help but feel a little blessed when he hears that other parts of the country experience single-digit and, in some cases, sub-zero temperatures.

There’s at least one hiccup to the moderate clime of Corpus Christi: For ranchers, the threat of parasite infection in cattle remains all year instead of, like in other parts of the country, tapering off during winter.

Parasites like warm weather. That means Texas ranchers have to be even more vigilant in the fight against the gangly, unwanted little pests that, when in cattle, hamper production and spike costs.

But no matter where you ranch – in a warm climate or cold – at one time or another during the year, you likely have to deal with the noxious little bugs that like to inflict cattle.

In some instances, parasite infestation can be fatal to cattle. They are especially severe to calves and older cattle.


“Heavy infestation can cause thinness and weakness in cattle,” says Paschal, livestock specialist with Texas A&M AgriLife. “They can impact weight gain, fertility and could kill the animal.”

As a general rule, adds Mac Devin, senior veterinarian for Boehringer Ingelheim, the younger the animal, the more pronounced the effect parasites have on the bovine. Severity, he says, depends on the number of parasites in the animal and what kind.

Treatments are available, but even then there’s no guarantee that all of the parasites are killed. In fact, it’s likely that some parasites will remain in cattle even after treatment.

“The idea is to keep the level of parasitism in check to keep the worm burden down,” Paschal says.

Enter anthelmintics, pharmaceutical drugs that kill helminthes (worms) – or at least most of them.

Just as there are many different kinds of parasite – worms and flatworms such as cattle liver flukes and deer flukes – there are several ways to introduce anthelmintics to cattle, including injection, liquid, paste and pour-on solutions.

Are some administrations more effective than others? That depends on the drug, Devin says. There are many different brands on the market, and some take effect more quickly than others. Talk to your veterinarian to see what he or she suggests.

“Some kill worms quickly; some kill worms slowly,” Paschal says. “I doubt any of them kill 100 percent of the worms. It has to touch or be ingested by the worm to kill it. … Some of them have a meat withdrawal time, so make sure you read the labels.”

Not all regions have the same parasites, so treatment might differ. Some breeds, such as the Brahman and other Bos indicus types, are more susceptible to resistance.

One thing is for certain: Anthelmintics for ruminants are just that – for cattle. They can harm humans, so caution should be used when administering.

Here are some tips before, during and after administering the products.

  • Testing: Testing animals for parasites is a simple process that involves collecting manure samples and taking them to a testing lab. Paschal suggests that newly purchased animals be tested.

    Be aware, however, that tests are not 100 percent. “There is no gold standard,” he says.

  • Weighing: If an animal or herd tests positive for infection, weigh the animals before administering an anthelmintic so you know the right dose to give.

    Don’t estimate; put the animal on a scale. “You might think he weighs 1,200 pounds, but he winds up weighing 1,500,” he says. The discrepancy could affect the outcome.

  • Administering: “You have some that are injectable, some that are pour-on, some that are liquid, some that are paste or like syrup, some that are feed, so you have all these different forms and how you administer them.

“They should never be ingested directly, not unless you have vodka and ice,” Paschal jokes. “But seriously, make sure they’re not ingested or splashed on your eyes, for instance. Make sure you don’t get them in or on you.”

Never administer an anthelmintic without first reading label instructions, especially its warnings. The products have come a long way over the years, says Devin, and they’re not harmful to humans as long as proper procedures are followed.

However, don’t assume that just because you’ve given one type of anthelmintic in the past that other forms of treatment are the same.

  • Storing: There are several different types of anthelmintic, thus storage of the products differ. “It really depends on the form,” Paschal says.

Feed-type dewormers come in sacks, so you’ll want to store them in a dry place off the ground.

Paste or pour-on solutions come in a tube or bottle. Keep them inside a cool area, away from extreme temperatures and out of the elements.

Many injectable solutions come in glass containers, so you’ll want to keep them out of direct sunlight and protect them from breaking and contamination.

Never put a used needle inside the product because of the risk of blood-borne diseases. Also, do not squirt air into the containers.

The same for pour-on solutions; protect them from sunlight and extreme heat.

If your dewormer comes in a large block, put it on a pallet off the ground and stored in a way that will keep it from raccoons, opossums, dogs and other animals.

You want to protect it from animal feces and saliva, Paschal says, but also protect animals from it. “It’s not something you want your dog to get into.”

  • Insecticides: Paschal says, “Insecticides to spray on the pastures or ranges might be costly (assuming there was one that worked) to spray, require additional time and might have restrictions. It is not used currently; nothing is cleared for use.”
  • Management: The single most important thing a rancher can do to minimize parasite infection is to manage his herd’s grazing. “If you’re grazing land intensively,” Paschal says, “you’re a pretty good candidate for having worm problems.”

He explains how parasite infection might spread: Worms in cattle pass through the GI tract to the manure that is left on the fields.

Helminthes eggs hatch, larvae crawl to the nearest blades of grass, cattle eat the grass and the infection spreads. A gram of feces may contain 10,000 eggs. Of that number, not many larvae survive, but it just takes a few to cause problems.

“If a rancher is relying 100 percent on anthelmintic use to kill parasites in his cattle, he needs to go back and look at his management style,” he says. “Sometimes a rancher will deworm an animal and then turn them right back to pasture.

That just allows them to pick up a new crop of worms. Instead, he suggests rotational grazing.

“Stomach worm larvae (or eggs for that matter) don’t live forever, so the longer the rest period of a previously grazed pasture, the more likely it is that they have been dried out or killed by lack of moisture or high heat or just flat run out of food and starved to death,” he says.

“The larvae have only a few hours after hatching to crawl up on a leaf and be ingested, so if there are no animals to ingest it (the pasture is being rested and the animals are in another pasture), the life cycle is interrupted.”

Rotational grazing helps fields to rest and regrow after grazing. Improved grasses need less rest, while native grasses need more time because they regrow slowly.

“That resting time helps kill the worms and break their life cycle,” Paschal says.

And that’s good news for any rancher, no matter the climate.